@mcc sometime when I get a package with duty to pay, I get an email with a link to pay it online, for cheaper than in person and if I do, they put it in my mailbox. The form behind the link only work after the package is processed at the duty office and before the delivery person show up the first time.
Sometimes I don't get the email. Sometimes I get it two day after I go to the post office to get the package. Usually, I can check the form and it work before I get the link